1. Field of the Invention
The present invention relates generally to speed change gear systems and more particularly to a speed change gear system which is suitable for application within fluid couplings or torque converters utilized upon motor vehicles, especially automobiles.
2. Description of the Prior Art
It is desirable that the auxiliary speed change gear system incorporated within automatic transmissions to be utilized upon large automotive vehicles, such as for example, trucks and buses, should have at least four speed shifts, and this may be realized by suitably combining three, four, or even more, sets of simple, single-pinion or double-pinion type planetary gear sets. The combination of these gears may be widely varied, but within any one particular combination, the following conditions should always be satisfied:
1. The output shaft should be coupled to the same elements within each speed range.
2. In order to reduce the circumferential speed of the bearings of each element of the planetary gear set, the number of revolutions should be small.
3. The tooth load, that is, the tangential force of each element should be small so as to maintain the strength of the gear teeth.
4. The gear set should meet the meshing conditions for the number of teeth employed. More particularly, the sun gear, whose diameter is to be minimized, as well as each planetary pinion gear, should have the necessary number of teeth.
5. With each planetary gear set, the coupling relationship among the elements should be simple and the distance from each other should be small.
6. During speed shifts wherein frictional coupling means are utilized during forward drive, such speed shifts should be available through one coupling means alone.
Present speed change gear systems do not satisfactorily attain all of the above-noted conditions with the requisite efficiency.